1. Field of the Invention
The present invention relates to sonic or acoustic tools including a calibration and/or testing device for tuning or calibrating acoustic receivers and associated electronics or testing the stability and integrity of acoustic receivers and associated electronics.
More particularly, the present invention relates to acoustic downhole tools including a transmitter, an isolator, a receiver, associated electronics and a calibration device for dynamic receiver calibration and receiver/electronic integrity and/or stability testing. The present invention also relates to methods of making and methods of using the tool.
2. Description of the Related Art
In general, the apparatus for making an acoustic log consists of a transmitter capable of providing acoustic impulses, and at least one receiver responsive to acoustic energy, both mounted on a support for movement through the length of a well bore. The transmitter and receiver are spaced apart by a fixed distance and as the support is moved through the well bore, the energy from the acoustic pulses periodically generated by the transmitter is picked up by the receiver after transmission through and reflection from the well bore. The amplitudes of the received signals are correlated with the depth in the well bore to provide a log indicating the qualities of the cement bonding to the bore over the length of the well.
The acoustic transmitter and receiver(s) employed for these purposes typically comprise a piezoelectric or magnetostrictive element which converts periodic electric impulses into acoustic waves corresponding to the frequency of the periodic electric impulses and having an amplitude generally proportional to the energy of the electric impulses. The receiver, on the other hand, receives acoustic waves impinging thereon converting the pressure waves into an electric signal generally proportional to the intensity of the acoustic wave energy or amplitude. Thus, the receiver and transmitters work essentially in the opposite format.
For effective operation of these components, it is necessary that they both be efficiently coupled to the surrounding media and at the same time carefully protected or insulated from deleterious effects of liquids and gases present in well bores or casing. As the tool move through the well bore, the tools will encounter numerous changes in heat and pressure and spurious acoustic and vibrational disturbances which can result in tool malfunctions or calibration drifts.
One major drawback to present acoustic or sonic tools is the lack of ability to calibrate or even test the receivers and associated electronics for integrity or stability during down hole operations. Numerous U.S. Patents disclose acoustic or sonic LWD tools including, for example, U.S. Pat. Nos. 3,213,415, 4,809,236, 5,197,038 and 5,485,431, but none address real time calibration and integrity testing of the receiver portion of the tool.
Therefore, there is a need in the art for improved sonic tools having receiver testing and calibration capabilities. Moreover, there is a need in the art for improved sonic tools allowing dynamic testing and/or tuning of the receivers incorporated in the tools. Furthermore, there is a need in the art for methods of testing receiver responses or to tune or calibrate the receivers during routine operation.